1. FIELD OF THE INVENTION
The present invention relates to optical glasses and more particularly to optical silicate glasses containing titanium dioxide which glasses have a high dispersion and a high index of refraction, as well as to a process of producing the same.
2. DESCRIPTION OF THE PRIOR ART
Optical glasses of high titanium dioxide content are known; but in all such glasses, large quantities of conventional glass formers are used. In addition alkali metal oxides, preferably those of sodium oxide and/or potassium oxide, are generally added to the known glasses. By the use of alkali metal oxides, the melts become rather thinly liquid and, as a result thereof, the melting, fining, and conditioning processes are favorably affected.
Such glasses, however, have indices of refraction which are lower than 1.7. As a result thereof, they are useful for certain optical systems to a limited extent only.
Titanium-containing glasses which contain silicon dioxide and boron trioxide as glass formers and furthermore a small proportion of alkali metal oxides, are also known.
These glasses, as a result of their low content of alkali metal oxides, are extremely strongly colored and thus cannot be used for optical purposes. Furthermore, the large proportion of conventional glass formers and alkali metal oxides, as is known, results in a relatively poor chemical stability. Glasses of the known type are in particular sensitive to a greater or lesser extent to hand perspiration and, therefore, on being processed in the optical industry, result in considerable amounts of rejects which in their turn cause an increase in the price of the corresponding products.